1. Field of the Invention
This invention relates to a method of identifying an object by detecting a contour line of the object to be detected by using an image pick up apparatus, for example, a television camera or the like.
2. Description of the Prior Art
A convertional method of identifying an article or object to be identified utilizes the edges of respective surfaces of the objects, and according to this method, the point of the picture image at which the brightness changes abruptly are extracted as the edges, and the edges are connected together to convert them into a line picture.
The steps of identifying a circular body with the contour line extraction method will be described with reference to FIGS. 1a through 1d. At first, an original picture image (shown in FIG. 1a) photographed with a television camera is differentiated along respective scanning lines to extract a contour candidate point at which the brightness changes rapidly (see FIG. 1b). Then, respective picture elements near this point are differentiated. Among the differentiated values, a picture element having the maximum differentiated value is taken as a point continuous to the contour candidate point. This processing is repeated a certain number of times to obtain continuous contour points (contour line candidate point) (see FIG. 1c) and when these candidate points are closed (see FIG. 1d), they are deemed as an object.
According to this prior art contour extraction method, however, the tracing of the contour candidate points are rendered difficult by the following factors:
(1) blooming caused by metal luster (see FIG. 2a),
(2) overlapping of objects (see FIG. 2b),
(3) vague or not clear image caused by rust, spoil, etc. of the object surfaces, and
(4) distortion of the picture image caused by electrical noise.
As a consequence, there is a defect that an actually presenting object would not be detected. Furthermore, identification algorithm for solving these problems becomes complicated so that real time processing is almost impossible.